1. Field of the Invention
The present invention relates to a mask holding device having a replaceable magnetic means, and a deposition apparatus for an organic light emitting device including the same, in which the mask holding device is provided with magnets, and the magnets can be replaced as required so as to change the magnetic force of the mask holding device.
2. Description of the Prior Art
As semiconductor industries and electronic display industries have rapidly developed, flat panel displays (FPDs), such as a Liquid Crystal Display (LCD) Device, a Plasma Display Panel (PDP), an Electro Luminescent Display (ELD), a Vacuum Fluorescent Display (VFD), and an Organic Light Emitting Display (OLED) Device, have been widely used in real life.
From among such FPDs, the OLED, which has been recently highly spotlighted, includes an anode, an organic layer, and a cathode stacked on a substrate. In an organic emitting layer (EL) included in the organic layer, recombination of a hole and an electron forms an exciton which emits light.
Methods for generating the organic layer as described above include a physical vapor deposition method, such as a vacuum evaporation method, an ion plating method and a sputtering method, a chemical vapor deposition (CVD) method through gas reaction, and the like. From these methods, the CVD method through gas reaction is widely used in order to form a thin film layer such as an organic film of an organic light emitting device. Also, for this purpose, a vacuum deposition apparatus using organic substances is mainly used.
In general, in a process for manufacturing a semiconductor device or an organic light emitting device, for fabrication of a thin film layer on a substrate, the substrate is attached to a substrate holder, a mask formed with openings, each having a desired shape, is positioned between an evaporation source and the substrate, and then the thin film layer is fabricated with a predetermined pattern on the substrate by using various methods, such as deposition.
In general, the mask is used to fabricate a thin film layer in a chamber while being, together with a substrate, attached to a substrate holder. In order to hold the mask, a mechanical fixing method or a magnetic fixing method is used. The mechanical fixing method employs a pin, a clip, or the like. The magnetic fixing method employs a permanent magnet or an electromagnet in order to hold a substrate and a mask, considering that the mask includes a magnetic material.
In such a conventional deposition apparatus employing a magnetic fixing method, in some cases, an appropriate magnetic force required for the size and the material of the mask and the substrate cannot be applied for fixing the mask on the substrate.
Moreover, an optimum magnetic force required for tightly attaching the mask on the substrate varies according to the size, the resolution, the type (e.g., slit type, dot type, etc.) and the material of the mask. Thus, it is necessary to supply an appropriate magnetic force according to the size, the resolution, the type and the material of the mask.
For example, when an excessively high magnetic force is used to bring the mask into contact with the substrate, wiring or barriers, which are formed in the substrate by photoresist or the like, may be damaged by an effect of the magnetic field. On the other hand, when a magnetic force is weaker than needed, it is impossible to properly attach the mask to the substrate.
Furthermore, in a conventional deposition apparatus, a magnetic means is attached to a structure within the chamber. In order to replace the magnetic means, the chamber is required to be vacuum-released and opened. Such vacuum-releasing and opening of the chamber may result in a great loss in view of a deposition process.
Accordingly, there is required a magnetic means which supplies an optimum magnetic force according to the size, the resolution, the type and the material of the mask, and which brings the mask into contact with the substrate while preventing the mask from being deformed by the magnetic force.